1. Field of the Invention
The present invention relates to a silica membrane and a method for manufacturing the silica membrane. More specifically, the present invention relates to a silica membrane having high separation performance and high permeability and to a method for manufacturing the silica membrane.
There is used a ceramic porous membrane made of a ceramic material excellent in corrosion resistance, such as silica, alumina, cordierite, mullite, and silicon carbide as a membrane for separating a specific component from a mixed liquid containing a plurality of liquid components, for example, a separation membrane used upon dehydrating alcohol, an organic solvent, or the like.
Such a ceramic porous membrane is formed by allowing the ceramic sol to adhere to the porous substrate, drying the ceramic sol, and firing and generally used unitarily with the porous substrate functioning as the support.
2. Description of Related Art
There is known a method where the acid resistance of the separation membrane is improved by setting the firing temperature to be high to suppress the decrease of water permeation amount with the passage of time (JP-A-4-63119). There is known a method where a membrane is formed by pouring a silica sol into a porous substrate by natural flowing as a method of adhesion of silica sol (WO No. 2008/050814 pamphlet). Further, it is known that the ceramic porous membrane having high separation performance can be obtained by the use of ceramic sol having a sol concentration of 0.05 to 0.7 mass % (JP-A-2009-241054). On the other hand, there is known a method where a coating liquid obtained by diluting a ceramic sol undiluted solution with isopropyl alcohol is allowed to adhere to the substrate and then drying the coating liquid by blast drying in order to obtain a ceramic porous membrane having few defects, a thin membrane thickness, and small pore size (JP-A-2008-246304).
However, the water permeation amount is not sufficient in the conventional method, and further increase in the water permeation amount is desired. In order to improve the water permeation amount, it is necessary to decrease the number of times the membrane is formed. However, the number of the number of the membrane formation times is decreased, the separation coefficient falls. In addition, there is a problem of decrease in the water permeation amount with the passage of time. This is because the organic solvent enters the membrane pores and is adsorbed to the surfaces to hinder the water permeation. If the firing temperature is raised in order to inhibit it, the pore size is decreased, and the organic solvent is inhibited to enter the pores. However, the permeation amount is decreased. In addition, firing at high temperature has a problem of increasing the production costs.